In a semiconductor memory device of the related art, a substrate is disposed within a casing. The casing includes a base that has a rectangular bottom wall and a side wall provided upright on an outer edge of the bottom wall, and a cover that covers an upper surface of the base. A positioning pin protruding in a direction toward the cover is disposed on an upper surface of the side wall of the base so that the base can be correctly positioned with respect to the cover.
According to the technique of the related art, however, a thickness of the side wall at a position at which the positioning pin is disposed is larger than that in other positions. Because of this, an area of the substrate disposed within the casing is reduced by as much as an area of a portion of the side wall in which the positioning pin is disposed.